1. Technical Field
The present disclosure relates to a line printer that moves the printhead between a position opposite the platen and a position removed to the side from the position opposite the platen, and to a method of moving a printhead in a line printer.
2. Related Art
A line printer that prints on recording paper conveyed at a constant speed over a platen is described in JP-A-2011-025479. The line printer in JP-A-2011-025479 uses an inkjet head as the printhead. The printhead is configured from a set of four inkjet line heads that respectively eject ink droplets of cyan, black, magenta, and yellow ink, and each inkjet line head is wider than the recording paper. The four inkjet line heads are disposed with a specific gap therebetween in the conveyance direction of the recording paper. The printhead is therefore large both widthwise to the recording paper and in the conveyance direction.
When the printhead is an ink jet head, print quality drops if the gap between the printhead and the platen is not held at a specific predetermined distance. The line printer described in JP-A-2011-025479 therefore has round posts that protrude from the printhead frame toward the platen side, and controls the gap between the printhead and the platen to the height of these posts by setting the bottom distal ends of the posts against the platen surface (the surface opposite the printhead).
When an inkjet head is used as the printhead, the ink nozzle face of the printhead is preferably capped by a head cap when the printer is in the standby mode. Capping can reduce evaporation of moisture from the ink through the ink nozzle face, and can prevent the viscosity of the ink in the nozzles from increasing. A flushing operation that discharges ink droplets from the printhead into the head cap at a regular interval is also desirable. The flushing operation can prevent the ink nozzles from clogging or unclog clogged nozzles.
In order to cap or flush the printhead in a line printer, a printhead standby position could conceivably be set beside the platen, and the printhead could be moved horizontally between a position opposite the platen and the printhead standby position, as in a serial printer. However, the printhead of a line printer may be rather large as described in JP-A-2011-025479. Because the area of the recording paper opposite the printhead at the platen increases when a large printhead is used, the recording paper can easily lift away from the platen when the printhead is retracted from the position opposite the platen. Therefore, when the printhead is then returned to the position opposite the platen, the printhead and the recording paper can collide, easily resulting in damage to the printhead or a paper jam.
To prevent the recording paper from lifting away from the platen, a star wheel or other media separation prevention member that pushes down on the recording paper as the paper passes over the platen may conceivably be provided. However, when such a media separation prevention member is provided, the media separation prevention member and the printhead may collide when the printhead moves horizontally from the printhead standby position to the position opposite the platen.
Furthermore, if the reference surface of the printhead unit (a surface parallel to the ink nozzle face of the printhead) and the platen surface are not parallel in a configuration that maintains the platen gap by setting posts protruding from the printhead unit against the platen surface as described in JP-A-2011-025479, the reference surface of the printhead unit and the surface of the platen are made parallel to each other by contact between the posts and the platen surface, which changes the posture of at least one of the printhead unit and the platen.
When the posture of the printhead unit and the platen changes due to contact between the posts and the platen surface, the posts move against the platen surface and the reference surface and platen are set parallel to each other. If the operation that forms the platen gap is performed repeatedly with the posts moving against the platen surface, the posts or the platen surface may become worn and forming a precise platen gap may not be possible.